1. Field of the Invention
The present invention relates to a thermal recording apparatus in which an ink of a melt type or a sublimation type provided on a recording medium is recorded on a recorded medium by heat, and specifically to a thermal recording apparatus using a serial head capable of being applied to a printer, a facsimile and a copying machine.
2. Description of the Related Art
Various recording apparatuses for obtaining images such as characters and natural pictures are available. A thermal recording apparatus in which an ink provided on an ink sheet ("recording medium") is recorded on a recording paper ("recorded medium") by heat by means of a recording head such as a thermal head is widely applied to various recording apparatuses. Such a thermal recording device has a simple mechanism, exhibits reliability, and is easy to maintain. For example, when a melt type or sublimation type ink sheet is used, recording is carried out by a pigment or dye ink by virtue of energy given to plural recording elements (thermal resistors) constituting a thermal head. A heating amount (heating energy) given to the heating elements described above is controlled by a number of electric pulses, a duration of such pulses and an applied voltage.
The constitution of such thermal recording apparatus is shown in, for example, Japanese Unexamined Patent Publication No. 62-117774. FIG. 17 is a schematic drawing for explaining this thermal recording apparatus, wherein 1 represents a recording head; 20 represents a platen roller; 3 represents a carriage for moving the recording head 1; 4 represents a guide shaft; 5 represents a recording medium comprising an ink sheet, wound on a feed roll 5a and a winding roll 5b; 6 represents a recording paper which is a recorded medium; and 7a and 7b represent guide rollers for the recording medium 5 described above.
The operation of the thermal recording apparatus constituted as described above shall be explained below. The recording head 1 carries out intended recording on the recorded medium 6 through the recording medium 5 by heating unillustrated recording elements (not shown) according to an image pattern. The recording head 1 is arranged opposite to the platen roller 20 extending in a main-scanning direction x. Further, the recording head 1 described above is mounted on the carriage 3 capable of running in the main-scanning direction x and moved along the guide shaft 4 disposed parallel to the shaft direction of the platen roller 20 described above while pressed on the platen roller 20 to carry out recording on the recorded medium 6.
To be specific, the recording medium 5 and the recorded medium 6 are present between the recording head 1 and the platen roller 20, and the recording medium 5 described above is stored in the carriage 3 described above and guided by the guide rollers 7a, 7b disposed on the both sides of the recording head 1 so that it contacts the recorded medium 6, whereby recording (1 band) according to the first main-scanning is carried out while being wound on the winding roll 5b from the feed roll 5a according to the main-scanning of the carriage 3. Then, the carriage 3 is returned to a start position (record starting position at the left side), and the recorded medium 6 is moved by the width of the recording head 1 by means of the platen roller 20 in a sub-scanning direction y to carry out the next main-scanning recording. Images are formed by repeating recording in the same manner.
Conventional thermal recording apparatuses are constituted as described above, and therefore there is the problem that stripes (white stripes in a main-scanning direction), or so-called banding, are formed between main-scannings to deteriorate image quality. This is caused by a structural factor originating in a drive accuracy of a recording head or a recorded medium and an uneven temperature distribution in which temperatures at the both ends of the recording head are lower than those of the central part thereof. A degradation in image quality can be solved by driving a recording head or a recorded medium at high accuracy and recording at high accuracy by correcting a temperature distribution in the recording head. In this case, however, the printing apparatus becomes expensive, large and complicated.
In the case of a thermal recording apparatus using a serial head, there is the problem that the running cost in terms of production is increased and the printing time is extended as compared with those of a recording apparatus using a line head. Further, in the case of a portable type thermal recording apparatus using a serial head, there is the problem of large power consumption.